1. Field of the Invention
The present invention relates to a multi-primary-color display device.
2. Description of the Related Art
A color display device such as a color TV monitor or a color display monitor represents colors usually by adding together the three primary colors of red (R), green (G) and blue (b). Generally, each pixel in a color display device has red, green and blue subpixels for these three primary colors of RGB. YCrCb (YCC) signals, which can be converted into RGB signals, are input to such a three-primary-color display device and the red, green and blue subpixels change their luminances (or grayscale values) in response to the YCrCb signals, thereby representing various colors.
The luminances of the respective subpixels vary within the range from the one corresponding to their lowest grayscale (e.g., grayscale level 0) through the one corresponding to their highest grayscale (e.g., grayscale level 255). If the grayscales of all of these subpixels, namely, the red, green and blue subpixels, is the lowest grayscale, the color represented by the pixel is black. Conversely, if the grayscales of all of these subpixels is the highest grayscale, the color represented by the pixel is white. Recently, TV sets are more and more often designed to allow the user to control the color temperature. In that case, the color temperature is controlled by finely adjusting the luminance of the respective subpixels. For that reason, the grayscale of the respective subpixels after the color temperature has been controlled to a desired value is the highest grayscale.
Although such three-primary-color display devices have been used generally so far, those display devices cannot represent fully a lot of colors discernible to human beings. To overcome such a problem, multi-primary-color display devices, which perform a display operation using four or more primary colors, have been proposed recently to expand the color reproduction range of display devices.
However, to make a pixel for such a multi-primary-color display device with the same resolution as a three-primary-color display device, a greater number of subpixels should be arranged either vertically or horizontally, thus causing an increase in cost. Meanwhile, if a multi-primary-color display device were fabricated with only the color filters changed and without changing the configurations of subpixels of a current three-primary-color display device, then the resolution would be lower than that of the three-primary-color display device and a display operation could not be performed with sufficiently high definition. In view of this consideration, a technique for increasing the resolution of a multi-primary-color display device in monochrome display mode has been proposed (see PCT International Application Japanese National Phase Publication No. 2005-523465, for example).
PCT International Application Japanese National Phase Publication No. 2005-523465 discloses a multi-primary-color display device including subpixels R, G, B, Ye and C in five primary colors that are arranged one-dimensionally as shown in FIG. 15. In such a multi-primary-color display device, each set of three subpixels that are adjacent to each other in the row direction, i.e., RGB, GBYe, BYeC, YeCR and CRG, can produce light that is as close to white light as possible, thus attempting to increase the resolution.
PCT International Application Japanese National Phase Publication No. 2005-523465 also discloses a multi-primary-color display device including subpixels R, G, B, C, M and Ye in six primary colors that are arranged two-dimensionally as shown in FIG. 16. In such a multi-primary-color display device, each pixel P has not only a subset T1 of three subpixels R, G and B representing the three primary colors of light in the row direction but also another subset T2 of three subpixels C, M and Ye representing the three primary colors of colors, which are arranged parallel to the subset T1. And each of these subsets T1 and T2 produces substantially white light. Also, in this arrangement, there are three pairs of subpixels RC, GM and BYe that are arranged in the row direction. Since the two colors of each of these combinations are complementary ones, substantially white light is also produced by each of these pairs of subpixels. In this manner, the multi-primary-color display device with the arrangement of subpixels shown in FIG. 16 tries to increase the resolution substantially threefold horizontally and substantially twofold vertically.
In the multi-primary-color display devices with the arrangements of subpixels shown in FIGS. 15 and 16, the subpixels are arranged such that the colors represented by the respective groups of adjacent subpixels have substantially the same chromaticity values. However, those colors represented by the respective groups of subpixels have mutually different luminances. That is to say, the luminances vary from one group of subpixels to another, and therefore, the resolution of the multi-primary-color display device cannot be increased substantively after all. Also, in representing an achromatic color such as white, if the upper limit of the luminance range adopted by a group of subpixels with a relatively high maximum luminance were set equal to a relatively low maximum luminance of another group of subpixels, then the variation in luminance between the groups of subpixels could be minimized. In that case, however, an achromatic color with a high luminance could not be represented.